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Ethernet Hot Standby Solution
172
840 USE 106 00 January 2003
Additional
Switchover
Information
The following list provides additional information about the NOE’s IP addressing
process resulting from a Hot Standby switchover.
Some MSTR/IEC Function blocks will not complete their transaction as a result
of the IP Address swap.
In this case, the MSTR/IEC Function block will return the error code 0x8000.
While the NOE is in the process of performing the above actions, a new MSTR/
IEC Function block may become active.
No resources are available to service the new MSTR/IEC Function block.
Therefore, the NOE will not service this new MSTR/IEC Function block, and all
three output lines will be low.
Going to Offline When either the CPU stops or the Hot Standby state goes to offline mode, two
events occur:
1. NOE mode goes to Offline
2. NOE uses the IP Address of the present configuration
IP Address Assignment and Going Offline
8 The Secondary NOE now becomes the Primary NOE.
9 Primary NOE opens all client connections and listens for all server connections
and re-establishes those connections.
10 Simultaneously, Secondary NOE listens for all server connections and re-
establishes those connections.
Step Action
HSBY State IP Address Assigned Is ...
Primary to Offline Configured IP Address, if other controller does not go to
Primary
Standby to Offline Configured IP Address + 1